Neuromuscular electrical stimulation (NMES), sometimes referred to as “functional electrical stimulation” or “FES”, is a technique by which muscles are induced to contract by application of electrical stimulation. NMES can be used along with exercise to strengthen an athlete's muscles, or it can be used therapeutically to strengthen and retrain muscles that have been weakened or damaged by disease or traumatic injury. NMES can also be used when voluntary motor ability is irretrievably lost, such as may arise from various forms of paralysis, to induce contractions that provide muscle benefits similar to that obtained by voluntary exercise. NMES may be distinguished from transcutaneous electrical nerve stimulation (TENS) which is used to treat pain by masking pain signals before they reach the brain.
Frequently, NMES has been applied in an attempt to activate muscles over which a patient has little or no conscious control. Thus, for example, U.S. Pat. No. 3,344,792 of Offner et al. describes a method and apparatus for applying NMES to the muscles of the lower leg to aid in walking. According to this patent, one electrode is placed on the skin over the tibialis anticus muscle and another is placed on the skin over the peroneus longus muscle. The two electrodes are then connected to a portable stimulator which is controlled by a pressure-responsive foot switch. The switch is opened when pressure is applied by the heel to the switch, and it is closed when pressure is removed. When the switch is closed, the stimulator unit applies brief pulses of current having a duration of 50 microseconds or less and an amplitude of 50 to several hundred milliamperes. The voltage required is generally on the order of 50-150 volts. As described in the Offner patent, the application of electrical stimulation in this manner not only serves as “a therapeutic method”, but also serves as “a substitute for the individual's own nervous system, providing effective utilization of the individual's muscles.”
U.S. Pat. No. 4,342,317 of Axelgaard describes a method and apparatus for applying neuromuscular electrical stimulation to the muscles in the thorax for correction of spinal curvature deficiencies. According to this patent, a pair of specific muscle sites within the muscle group to be treated are selected, so that stimulation of the two muscle sites, on an alternating basis, will not result in any overlap of stimulation. A dual channel alternating stimulator is employed to generate alternating ON/OFF waveforms for each channel. The amplitude of the stimulating pulses is within the range of 60-80 milliamperes, and the ON/OFF times for each of the two channels are adjusted so that one muscle group starts to contract while the other starts to relax, and vice-versa.
U.S. Pat. No. 4,392,496 of Stanton describes a dual-channel neuromuscular electrical stimulator which is adapted for neuromuscular stimulation at two sites for exercising muscles to prevent disuse atrophy while minimizing fatigue. The stimulator provides, on two output channels, alternating pulsed stimulation signals which are increased in intensity at a variable rate until a fixed intensity is reached. The pulses are applied during an adjustable predetermined stimulation period and removed during an adjustable predetermined resting interval. In the preferred embodiment of the invention, the pulse rate is adjustable between 3 and 50 pulses per second.
U.S. Pat. No. 4,569,352 of Petrofsky et al. describes a feedback control system that employs a plurality of sensors and electrodes through which neuromuscular electrical stimulation is applied to enable standing and walking by paraplegic and quadriplegic persons. A programmed microprocessor produces hip movement by generating control signals for stimulation transducers which stimulate the iliacus and hamstring muscles. Knee flexion is produced by transducers which stimulate the quadriceps muscles, and ankle movement is produced by stimulating the gastrocnemius and tibialis muscles. The stimulation circuitry creates a series of alternating pulses at a frequency of 50 Hz.
U.S. Pat. No. 4,586,495 of Petrofsky describes a method and apparatus for stimulating the muscles of a patient who has suffered a spinal cord injury during the period following the injury and prior to the time when stimulated dynamic exercise may be commenced according to the method and apparatus of U.S. Pat. No. 4,569,352. The apparatus of the '495 patent includes a leg brace which maintains the knee and ankle at predetermined angles. Electrodes are applied to the muscles of the braced leg over the agonist and antagonist muscles for bending the leg about the knee and ankle joints. The hamstring and quadriceps muscles function as agonist and antagonist muscles, respectively, for the knee joint and the tibialis anterior and gastrocnemius muscles function as agonist and antagonist muscles, respectively, for the ankle joint. In the preferred embodiment of the invention, the quadriceps muscles are stimulated for approximately four seconds to cause the muscles to attempt extension against the restraint of the brace. Thereafter, the quadriceps muscles are rested and the hamstring muscles are stimulated for four seconds to cause the muscles to attempt to bend the knee against the restraint of the brace. Then both sets of muscles are rested for four seconds, and the sequence is repeated. After the hamstring and quadriceps muscles have been exercised, the electrodes are placed on the tibialis anterior and gastrocnemius muscles and a similar stimulation sequence is begun for these muscles. A pair of load cells on the leg brace provide feedback signals to a computer which controls the application of the electrical stimulation signals. As the muscles tire with exertion, the computer increases the stimulation level until a maximum value of 50 volts is reached. Each stimulation signal comprises a series of pulses having a pulse width of about 300 microseconds and a frequency of 40 pulses/second.
As mentioned above, NMES can be used along with exercise to strengthen an athlete's muscles, or it can be used therapeutically to strengthen and retrain muscles that have been weakened or damaged by disease or traumatic injury. Thus, for example, U.S. Pat. No. 4,622,973 of Agarwala describes a clinical device which may be used to establish an NMES regimen, as well as a portable device which is programmable by the clinical device and which automatically reproduces the NMES regimen which was established in the clinical device.
U.S. Pat. No. 4,996,987 of Petrofsky describes a method and apparatus for applying electrical stimulation to induce work-producing contraction of the muscles. According to this patent, the stimulation of work-producing contraction of muscles in patients with little or no nerve damage causes unacceptable pain. Consequently, the method of the invention includes applying a high-frequency, low-amplitude desensitizing current to the muscle to be stimulated prior to applying a low-frequency, high-amplitude stimulating current which is continuous with the desensitizing current. The stimulating current is applied as the desensitizing current is terminated, and the two currents are alternately applied so that no abrupt discontinuity occurs between the currents. Preferably, the stimulating current is a “camel-back” biphasic signal having three segments, the first and third of which are of opposite polarity to the second. The first and third segments are substantially identical in duration and magnitude, and the second has a duration equal to the sum of the durations of the first and third segments and a magnitude that is equal to and of opposite polarity to either the first or the third segment.
U.S. Pat. No. 5,562,718 of Palermo describes a device for use in applying NMES in a series of electrical pulses in the form of sequential pulse patterns, or dual or triple overlapping pulse patterns. These electrical pulse patterns are applied through a first channel by electrodes that are attached to the skin over an agonist muscle and through a second channel by electrodes that are attached to the skin over the corresponding antagonist muscle. The timing of the sequential or overlapping pulse train patterns is reportedly selected to take advantage of central nervous system inhibition and facilitation by repetitive cycling of the pulse trains to emulate reciprocating limb speeds ranging from slow gentle arm or leg movements to the fastest running patterns. The commercial embodiment of the Palermo device, marketed by Accelerated Care Plus of Reno, Nev., employs electrodes applied to the agonist and antagonist muscles to generate overlapping pulse patterns that serve to contract these muscles. According to literature published by Accelerated Care Plus, a first pulse pattern is applied through a first channel to the agonist muscle in a first burst period of approximately 75 msec., followed by a first rest interval of about 50 msec. and a second pulse pattern in a second burst period of about 50 msec. A third pulse pattern is then delivered to the antagonist muscle through the second channel in a third burst period of about 75 msec., which begins approximately 55 msec. after the beginning of the first burst period (of the first channel) and continues through the first rest interval (of the first channel) and for about 10 msec. into the second burst period.
U.S. Pat. No. 5,980,435 of Joutras et al. describes a method and apparatus for therapeutic use of a jointed brace. According to this patent, the brace is attached to a jointed limb and provides controlled resistance to movement of the limb about the joint. The brace may used in conjunction with a neuromuscular stimulation device, and it may be programmed to resist the movement of stronger, or antagonistic, muscles against weaker, or agonistic, muscles. However, there is no force applied by the equipment to the user in the absence of an attempt to move a limb about a joint. The force applied by the equipment is only a force of reaction.
U.S. Pat. No. 6,845,271 of Fang et al. describes a method and apparatus for treatment of shoulder dysfunction using neuromuscular electrical stimulation applied through intramuscular electrodes. Preferably, the method involves asynchronous stimulation of more than one muscle group, such as a first muscle group being the supraspinatus in combination with the middle deltoid and a second muscle group being the trapezious in combination with the posterior deltoid. This asynchronous stimulation involves intermittent periods of stimulation and rest, with one muscle group being subjected to stimulation while the other is resting.
Although it is known to apply NMES to the agonist and corresponding antagonist muscles in certain pulse patterns, the inventors have developed a method and apparatus for generating NMES pulses in patterns that appear to more accurately simulate natural movement of a limb about a joint.